1. Field of the invention
This invention relates in general to monitoring pressure remotely, and in particular to an optic fiber pressure transducer having reference and sensing legs and a temperature compensating device for compensating for temperature changes.
2. Description of the Prior Art
There are instances where remote sensing of pressure is a difficult task. For example, in oil, gas or steam wells a typical pressure sensor will mount within the well. Electrical lines will supply power to the sensor to monitor the pressure. Having active electronics in a well environment can be a problem. High temperatures in the well can affect the electronics adversely. Immersion of the electrical cable in the well environment, which is harsh, can cause cable failure.
U.S. Pat. No. 4,859,844 describes a pressure sensing system that utilizes an optical interferometer. The system in the patent employs fiber optics. Light is transmitted through optic fibers. The light splits at an optical coupler/splitter into two legs. One leg is used as a reference. The other optic fiber leg has one end connected to a bourdon tube or other type of pressure transducer.
A difference in pressure sensed by the pressure transducer will cause a change in length of the sensing leg. The light passing through the sensing and reference legs reflects back to the splitter. If the length in the sensing leg changes as a result of pressure change, then the light path length travelled in each leg will not precisely match. This difference can be processed by conventional equipment. The differences can be correlated into the pressure sensed.
The temperature in a downhole well will be elevated. If the temperature changes, both the reference leg and the sensing leg will experience a change in length due to the temperature change. The bourdon tube will also experience a change in length due to temperature effect. The temperature effect could be misread as a pressure change.